A witness saw Plaskon on top of the 16-year-old victim during the attack, and tried unsuccessfully to pull him away, and another saw him discard a bloody knife, according to a police affidavit. Plaskon was inside the principal’s office with bloody clothes when an officer arrived and asked what happened. “I did it. Just arrest me,” Plaskon replied, according to the officer.

Plaskon was arraigned Tuesday at a medical facility, where his attorneys say he has been undergoing psychiatric evaluation.

State’s Attorney Kevin Lawlor decided Plaskon will be prosecuted as an adult, and not in juvenile court. The next court hearing is scheduled for Friday in Milford Superior Court.

Plaskon is to be transferred to the custody of the Correction Department, with bond set at $3 million. A judge called for Plaskon to be held in age-appropriate conditions with continued psychiatric attention.

The attack occurred last Friday, hours before the school’s junior prom, and police have been investigating whether it was related to Sanchez’s refusal to be Plaskon’s prom date.

Plaskon’s family said Tuesday it joins the community in mourning the loss of life as it struggles to understand what led to the crime.

“Words can only fall short in conveying the depth and breadth of the raw sadness we are left with by this unimaginable tragedy,” the family said. “We join with the entire Milford community to celebrate the life and mourn the loss of this most vibrant and exceptional young woman.”

His family thanked relatives, friends and neighbors for reaching out to them in what they called their darkest hour.

“We pray for the wisdom to guide us as we desperately try to pull together the shattered pieces of our families,” the family said.